Industrial gear units are generally conventional which include lubricant that must be poured in or removed and exchanged during assembly and/or servicing. Therefore, many gear units have a tapped hole in their housing which is closed by a screw plug. To save space, this is provided with a hexagonal recess so that it does not protrude at all or protrudes as little as possible from the housing.
German Published Patent Application No. 198 42 173 describes a fastening element having a self-locating screw connection. A vibration sensor is able to be mounted on the fastening element.
A disadvantage in that case is that it is not possible to screw in the vibration sensor, since the fastening element has a bore hole starting from the base (FIG. 1 of German Published Patent Application No. 198 42 173, reference numeral 32) for improving the elasticity of the fastening element (German Published Patent Application No. 198 42 173, column 3, lines 41-45). The vibration sensor is thus pasted on or the like. Therefore, the structure-borne noise to be detected must be transmitted through the screw thread and the core (German Published Patent Application No. 198 42 173, reference numeral 22) and the adhesive connection. Consequently, only a single essential path exists for the sound, and it is not possible to achieve a good signal-to-noise ratio, since each junction, i.e., each connecting point, worsens the signal-to-noise ratio. It is also disadvantageous that when screwing in the fastening element, shavings develop which trigger oil contamination and later, even destruction of a device. In addition, because of the conical design, the axial guidance during the screw-in operation is poor. Therefore, the fastening element is at an unpredictable angle, and signal-to-noise ratios of different quality come about for the sensor signals depending on the angle. In the same manner, there is no defined stop face, and therefore also no defined pressure. As a result, the sealing function is also not defined, and the signal-to-noise ratios fluctuate for the same reasons, as well. There is also no reuse capability, since each time the fastening element is loosened and screwed in again, it sits ever more loosely in the base. Moreover, there is even the danger that if the tightening torque is too great, the O-ring (German Published Patent Application No. 198 42 173, reference numeral 4) will be destroyed, and therefore the sealing function can no longer be reliably ensured. In addition, the surface of the base and of the hexagon head is not machined, and already for this reason, a sealing function cannot be ensured.
It is an aspect of the present invention to provide as compact and cost-effective a production series of gear units as possible, in which gear units having vibration sensors may be also included, and which may provide great flexibility for meeting customer wishes.